The Twenty-fourth Dieron Regulars were one of thirty-one regiments of Dieron Regulars to be created by the Draconis Combine Mustered Soldiery after 2765.[4] The Dieron Regulars expanded by ten regiments during the Amaris Civil War,[5] and a further twenty-one regiments were raised between the end of the Civil War and the end of the First Succession War. Of the latter twenty-one regiments, eight were formed by recruiting Star League Defense Force personnel and units - including the Twenty-fourth - whilst the remainder were recruited more conventionally.[4] Some of the regiments of Dieron Regulars recruited from the SLDF were complete commands recruited wholesale, but others - like the Twenty-fourth - were ad hoc formations. The Twenty-fifth was one of the first DCMS regiments to be founded using SLDF personnel; the regiment was establised in 2782 using a regiment of troops recruited from the former Twenty-ninth Mechanized Infantry Division.[1] Originally one of the divisions within II Corps,[6] a part of the Twelfth Army,[1][6] the Twenty-ninth had been disbanded as an operational command following heavy losses during the Periphery Uprising, but the surviving elements of the division had continued to fight throughout the Hegemony Campaign.[6]

The Twenty-fourth was one of the units to take part in the Third Battle of Mallory's World in 3013 supporting the elite Second Sword of Light regiment.[7] Their first combat on the world occurred outside a reservoir where they fought the Seventeenth Avalon Hussars. The Hussars executed a surprise combat drop, but the sheer number of armor and infantry units attached to the Twenty-fourth quickly overwhelmed the Hussars.[8] A few months later the Twenty-fourth tried to sack a city defended by the weakened Fourth Davion Guards, Seventeenth Avalon Hussars, and the Kell Hounds. Though they were able to occupy their old defensive positions, the Regulars didn't realize that these positions had been booby-trapped by the Federated forces. When they tried to withdraw from these trapped fortifications, the AFFS units slammed into them and inflicted serious losses. The Twenty-fourth was able to break through the defenders however, and left the world in December 3013, after the death of First PrinceIan Davion.[9]

In 3016 the Twenty-fourth returned to Mallory's World. Their first assault at that time centered on their old foes the Seventeenth Avalon Hussars. Landing around the Hussars base in Colterville, the Regulars were inflicting serious losses on the Federated RCT when the order to evacuate the planet arrived. Though a draw, the Twenty-fourth inflicted enough damage on Colterville that the planetary capital had to move to Mallory City.[10]

The Twenty-fourth was deployed alongside the Fifth Sword of Light in the counter-attack on Pike IV in July 3039, arriving on the 19th. In contrast with the Fifth Sword of Light, the Twenty-fourth was considered an inexperienced command and used for security work or as cannon fodder. Pike IV was being held by the Thirtieth Lyran GuardsRCT and the mercenary unit Hansen's Roughriders, who had been heavily committed to dealing with the continuing insurrection going on amongst the divided highlander and lowlander populations on the planet, and avoided direct combat for more than two weeks until a battalion of the Roughriders was cornered in the mining settlement of Mercator by the Fifth. The Fifth's attack destroyed more than half of the Roughrider's forces in Mercator, whilst also inflicting substantial damage on the settlement and further alienating the highlander population against the Combine. By late August the Fifth had seized control of the remainder of the continent of Karasia and left a battalion from the Twenty-fourth there as a garrison force, while moving the remaining Combine forces against the Roughriders defensive positions. The Roughriders had used the time available to them to fortify and reinforce their positions, and had also been reinforced from off-world a few days before the first major DCMS attack, as the Seventeenth Skye Rangers had redeployed to Pike IV from Kervil, blasting through the orbital pickets above Pike IV and taking defensive positions around the city of Stratopolis.[11]

Sho-shoJonathan Fujimoto assigned the second battalion of the Fifth Sword to attack Stratopolis, but the deep raid led by Chu-saHohiro Tatsuma failed in the face of a ferocious defense mounted by the Rangers and Roughriders that far exceeded the resistance expected - including anti-Mech attacks being launched against lighter Sword 'Mechs by LCAF infantry units. Attempts by the ISF to assist the Fifth Sword and the Twenty-fourth by inciting an insurrection amongst the highlander population failed, and the LCAF units swiftly launched a counter-offensive of their own. With both sides facing stretched supply lines and the Lyran commands quickly gaining superiority in the air, the campaign stabilised around a front three hundred kilometers south of Stratopolis; although the Fifth and Twenty-fourth were in a position to keep fighting, the DCMS units were slowly ground down and by October an eventual Lyran victory seemed certain. It was at that point that recall orders were issued, cancelling the invasion of the Draconis Combine; while the senior LCAF officer on Pike IV was incredulous at being ordered to abandon Pike IV despite victory clearly being on the horizon, the Roughrider's contract ended on the 6th of November, with Colonel Hansen withdrawing his troops shortly after. That left the Lyran position in a precarious state, and the Thirtieth Lyran Guards and Seventeenth Skye Rangers withdrew over the next ten days, leaving the Fifth Sword and Twenty-fourth Dieron Regulars in control of Pike IV. Feeling that the performance of the DCMS units on Pike IV was a stain on his honor, Sho-sho Fujimoto petitioned the Coordinator for permission to commit seppuku; his petition was granted, despite KanreiTheodore Kurita considering it a waste of an excellent officer, and both units began the task of rebuilding.[11]

In 3050 the Twenty-fourth Dieron Regulars were stationed on Algedi.[12] The Twenty-fourth was one of a number of regiments to be carved up to help form new or replacement commands in the immediate aftermath of Operation REVIVAL, with elements of the Twenty-fourth being hived off to form the Forty-fifth Dieron Regulars. Conventional forces from Herndon were assigned to the Twenty-fourth on a temporary basis while the regiment awaited the allocation of formal replacements from the Bureau of Substitution, but the Twenty-fourth's ability to deploy was limited was the Herndon contingent couldn't be deployed off-world. The new commanding officer of the Twenty-fourth, Tai-sa Akihito, spent five years as an instructor at the Sun Zhang Academy and was an experienced training officer; as a consequence he swiftly implemented a rigorous daily training schedule within the Twenty-fourth soon after his arrival, although Dai-i Metsuichi, the commanding officer of the Twenty-fourth's aerospace forces, received considerable leeway from Akihito despite Metsuichi's hot temper because of Metsuichi's ability to get results.[13]

The Twenty-fourth had greater endurance than many other units because the majority of the 'Mechs within the command had at least one permanently-mounted energy weapon, reducing the command's dependence on ammunition; this also extended to the Twenty-fourth's aerospace wing, the majority of which were configured to use energy weapons. The Twenty-fourth had relatively few assault-weight and light-weight lances, but those assault-weight lances were used as anchor points during battle, while the light lances were used for scouting. In a departure from more conventional tactics, the Archers and Catapults within the Twenty-fourth frequently waded directly into battle when they had exhausted their ammunition, often accompanied by armour. Under Metsuichi's command the Twenty-fourth's aerospace forces trained extensively for making daring, steep-angle strafing runs on enemy 'Mechs.[13]